Advertisement referral based on social ties

A method of targeting a user of a network-based service with at least one monetization opportunity, comprising:

• processing characteristics of the user relative to a targeting model, wherein a characteristic being processed includes an indication of a monetization opportunity referred to the user by a referring user;
• based at least in part on the processing, determining the at least one monetization opportunity.

A method of maintaining a user information collection system usable by a targeting model to determine whether to target a particular user who has been referred a particular monetization opportunity by a particular referring user with whom the particular user has a social tie, comprising:

• maintaining a targeting weight for the referral associated with the user and the particular monetization opportunity;
• and
• adjusting the targeting weight for the referral to the particular user based at least in part on an amount of lift achieved as a result of referral of the particular monetization opportunity to users other than to the particular user.

A system configured to refer monetization opportunities, comprising at least one computing device configured to:

• determine that a particular user of network-based services has been presented a monetization opportunity offered to the particular user via a computer network;
• based at least in part on the determination, cause a monetization opportunity to be referred, via the computer network, to at least one other user of the network-based services, other than the particular user, with whom the particular user has social ties.